U.S. sales volume of carbonated soft drinks fell 3 percent in 2013, according to an annual report by Beverage Digest, an industry tracker. That represents a steeper drop than the 1.2 percent decline in 2012 and the 1 percent drop in 2011.

Carbonated soft drinks still represent the biggest category in the beverage industry. But the popularity of Coke, Pepsi and other soft drinks is waning as alternatives like flavored waters pop up in beverage aisles. Soda's unhealthy image has also hurt sales.

Diet sodas are also falling at a faster rate than their regular counterparts. Industry executives blame the trend on worries people have about artificial sweeteners.